BS 4718:1971

Co-operating organizations
Foreword
Methods of test
1 General
1.1 Scope
1.2 General
1.3 Definitions
1.4 Symbols
1.5 Instrumentation
1.6 Installation
1.7 Quantities to be measured
1.8 Methods of measurement
1.9 Thermal environment
1.10 Accuracy of measurements
2 Measurement of static insertion loss
2.1 General requirements
2.2 The in-duct method
2.3 The diffuse field method
3 Measurement of generated noise loss
3.1 General requirements
3.2 Diffuse field: direct method
3.3 Diffuse field: substitution method
4 Measurement of pressure loss
4.1 Test methods
4.2 Presentation of results
Appendices
A Calculation of mean band sound pressure level
B End reflection
C Typical coupler and anechoic termination
D Illustration of reference sound source
E Extrapolation from results of individual tests
F Measurement of casing radiation
Figures
1 Substitution duct arrangements
2 Arrangement of test installation for in-duct tests
3 Microphone positions at in-duct measuring plane
4 Arrangement of test installation: diffuse field
      method
5 Typical arrangement of installation for generated
      noise level measurement
6 Positioning of reference sound source, diffuse
      field substitution method
7 Installation for pressure loss measurements

Measurement of performance of unit silencers and silencing elements for ducted ventilating and air conditioning systems; aspects considered are attenuation of broad band airborne sound (insertion loss), generation of aerodynamic noise (generated noise level) by, and change in pressure in, air flowing through silencer. Methods measure insertion loss without airflow. Does not apply to silencers providing selective attenuation over narrow frequency bands, or to silencers designed for direct coupling to a fan or for sound insulation of partitions with ventilated openings.